They are dark, spider-shaped structures of branching fractal depressions found exclusively in the southern polar regions of Mars. They are so mysterious that we are sure that there is nothing like it on Earth or on any other planet in the solar system. How are they formed?
While it is true that there are a number of landforms on Mars that do not have their terrestrial equivalent such as Mount Olympus , the largest known volcano in the solar system or gorges such as Valles Marineris . the ice sheets of the polar regions, the seasonal channels in the crater walls or the “ghost dunes” , the “spiders” are among the strangest of all.
Now, a team of scientists from Trinity College Dublin seems to have found the key to the enigma by providing the first physical evidence that these unique formations on the planet’s surface, the “Martian spiders”, can be formed by sublimating ice from CO2.
Unlike Earth, the atmosphere of Mars is made primarily of carbon dioxide, which is deposited on the planet’s surface in the form of ice and CO2 frost (dry ice) when temperatures drop in winter.
Confirmed: Sublimation of carbon dioxide ice plays a central role in the formation of Martian spiders
This structure has been observed mainly in the ice sheets of the South Pole region and the surrounding plains. In themselves, they consist of a central depression from which radially meandering areas start, often branched, like tree branches or lightning bolts, which remind us of the legs of terrestrial spiders. If we increase the distance from the center, they become flatter. Sometimes we even see them overlapping, or in groups. They are usually accompanied by dark spots and fan-shaped shapes; a scene that can extend over tens of meters or even a kilometer.
“These features, which are not found on Earth, are believed to be carved into the Martian surface by the direct change of dry ice from solid to gas (sublimation) during spring,” the researchers state in their study published in the journal. Scientific Reports.
It is the first time that it is shown
The experts carried out a series of experiments in the Open University’s Mars Simulation Chamber “to investigate whether patterns similar to Martian spiders could be formed by sublimation of dry ice.” So it was . Under Martian atmospheric pressure, the blocks formed a gaseous layer around them as they hit the sandy surface. All of this left behind an eroded spider pattern. The sublimation was “much more vigorous than expected,” the researchers said, and material was thrown throughout the chamber.
“This research presents the first set of empirical evidence for a surface process believed to modify the polar landscape on Mars. The experiments directly show that the spider patterns we observe on Mars from orbit can be carved out by direct conversion of dry ice from solid to gas . It is exciting because we are beginning to understand more about how the surface of Mars is changing seasonally today, “says Lauren McKeown, leader of the work.
These findings will be of great interest to any future robotic or human exploration of the planet and suggest that geomorphic processes on Mars still have some secrets up their sleeves.
Referencia: Lauren Mc Keown, J. N. McElwaine, M. C. Bourke, M. E. Sylvest, M. R. Patel. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric pressure. Scientific Reports, 2021; 11 (1) DOI: 10.1038/s41598-021-82763-7
